It is probably a Chileanicon Mauser made in Germanyicon for export. The original caliber is 7mm. It isn't a common cartridge anymore but isn't that hard to find either, there are a lot of them in the country. There should be a crest on the top of the receiver. Compare it to some photos on the web to confirm.

I'd steer clear of the 308 conversions because these rifles are not strong enough to handle that caliber. The metal in the receiver will stretch over time because of the added pressures.

Sportsman's Guide prices are a bit high for these too so be careful.

I picked one up at a local gun shop for $120 about 6 months ago, all matching numbers and excellent condition metal. Only problem was the stock which was filthy but it cleaned up very nice.

Ammo is not impossible to find. The larger distributors should carry it. It's a bit more costly than the common calibers but on par with most of the older ones. Cabelas sells it for about $22 per box of 20.